Pine Bark BeetlesCooperative
Extension, College of Agriculture & Life Sciences, The University of Arizona

Written by
Tom DeGomez, County Agent
Deborah Young, Associate Director

Pine bark beetles in Arizona are generally of the genus
Ips or Dendroctonus. However, several other genera also attack pine, including:
Hylastes, Hylurgops, and Pityogenes. Often several species will attack
at the same time. Identification of specific beetle species can be difficult.
Identification can be aided by knowing the host species attacked, time
of year, and the design of the galleries (tunnels) created by the adults
and larvae.

Bark beetles contribute to the death of thousands of ponderosa
pines in Arizona each year. Most often when larger trees are attacked
and killed they have been weakened by drought, lightning, construction
activity or they have been growing on poor sites. Of special concern is
the loss of high-value trees at home sites or in developed recreation
areas.

Evidence of infestation

Fading foliage in the tree is often the first sign of a beetle
attack. Trees attacked by Ips spp. typically fade from the top of
the crown downward, while Dendroctonus spp. killed trees fade from
the bottom of the crown upward. The needles change from green to
a light straw color within a few weeks to one year after attack
and eventually become brown or red. Dust caused by boring in the
bark crevices and at the tree base is another sign. Often, numerous
small pitch tubes globules of pitch ³/4 to 1 ¹/4 "
diameter) appear on the trunk of infested trees.

Figure 1.Typical bark beetles are 3/16 - 1/4" (4-6 mm) in length

The pitch tubes generally have a creamy
appearance, much like crystallized honey. A pink or red tint may be
present in the pitch. The presence of one or two pitch tubes may not
mean that a beetle was successful. Often a few pitch tubes can indicate
that the tree successfully repelled the attacking beetle. Clear sap
that runs down the bole (trunk) or limbs is generally not from bark
beetles.

Life history

Life history varies with each species; the following description is true
for most. Beetles become active in April and early May. Adults emerge
from trees, slash, or firewood infested the previous fall. Adults prefer
freshly cut green trees or trees stressed from drought but when a large
number of beetles are present, they attack live pines. Ips spp. beetles
characteristically attack the upper portion of the tree, but when beetles
are abundant, the entire tree can be invaded and killed. Several species
will only attack the base of the bole (see Table 1).

Adults bore through the outer bark and then tunnel and lay eggs in the
soft inner bark. Eggs hatch in about a week and larva feed on the inner
bark for six to eight weeks before they pupate. It is the boring activity
of the adults and larvae that kills trees by girdling in combination with
stain fungi the beetles introduce. The development of larvae and pupae
of some beetles is completed in the outer bark. Adults develop from pupae
and emerge by boring out through the bark. After emergence, adults fly
and attack freshly cut material or susceptible trees and start the next
generation. Most beetles produce one to two generations each year but
some may have three or four. The overlap of generations during the summer
may produce continuous attacks.

Table 1.
Dendroctonus and Ips Species that Attack Pines in Arizona

Species

Hosts

Comments

Dendroctonus adjunctus roundheaded pine beetle

Pinus ponderosa, P. flexilis

Attacks the basal portion of the bole of overstocked
and pole sized trees. Flies during the fall.

Freshly cut ponderosa pine slash and firewood are subject
to attack by bark beetles. The success of beetle attacks and production
of young beetles are greatly influenced by when trees are cut. Trees cut
during the late summer and fall are seldom successfully attacked, because
the inner bark dries during the fall and winter. The inner bark of green
trees cut from January to July remains moist and suitable for beetle habitat.
An exception to this is the roundheaded pine beetle, which flies during
the fall, and attacks trees at that time. The Arizona State Land Department
found this beetle attacking trees near homes in the Santa Catalina Mountains.
Roundheaded pine beetle activity was found near trees that had been thinned
and chipped in October.

The slash and limbs of green pine trees should be buried
or burned (according to safe conditions and laws) within 30 days after
a tree has been cut down. The bole of the tree should receive the same
treatment, unless it is needed for firewood or poles. Then the material
should be piled away from living pine trees and covered securely to the
ground with heavy, clear plastic. The plastic covering should be left
on the pile at least 60 days if the trees are cut during the April though
October period. Heat builds up under the plastic and kills or traps the
beetles. This treatment also dries the inner bark limiting the food for
the beetles. Trees cut in winter should be used in a fireplace or disposed
of before April. If not used, the firewood that is left at the end of
March should be covered for 60 days. If logs are to be used as poles they
should be pealed as soon as possible.

Once a beetle build-up starts in the neighborhood all live
pine trees are targets for an attack, but some trees are easier targets
than others. Trees that have been damaged or weakened by blasting, excavation,
raising of the soil grade, lightning, disease, lack of water, septic systems,
or other stresses are usually not able to withstand an attack as well
as healthy trees. An attack by the beetle may not be detected until the
beetle has completed its life cycle and the tree starts to fade and die.
At this time, the beetle build-up can be stopped if the tree is immediately
cut and the material treated within a few days as described above.

Figures 2 & 3.Bark Beetle Killed Trees

There are no practical and effective sprays or injections to stop an
attack on green trees. Insecticides are not recommended once bark beetles
have successfully attacked. Un-infested trees can be protected from beetle
attacks by spraying with insecticides. When spraying, the entire trunk
of the tree up to 4" diameter must be covered. This is a protective
measure only. Insecticide will not kill beetles once they enter the tree.
The available chemicals for this purpose can vary from year to year. You
must use a product that is especially formulated for bark beetles. Typical
home and garden insecticides will be ineffective. Check with your local
county Extension office for current recommendations on the proper insecticides
to use as a preventive measure.

Healthy trees offer some resistance to attack. Watering during dry periods
(when less than 2 in. of moisture per month occurs) can help keep trees
healthy. Thinning out dense stands of trees will make more water available
for the remaining trees. Insecticides can be sprayed on the bole of the
tree to prevent initial attack by beetles. This must be done prior to
beetle emergence in the spring to be effective.

A fading crown and boring dust are the surest signs that a live tree
has been attacked. When the entire crown begins to fade, there is no hope
of saving the tree, and it should be removed as quickly as possible to
prevent emerging beetles from attacking other trees. Once the entire crown
has turned yellowish brown, it is generally too late to stop the spread
because the beetles have already flown to attack nearby trees.

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by the University of Arizona.
Document located http://cals.arizona.edu/pubs/natresources/az1300/
Published November 2002Return to College publication list